fix(coordination): accept a sticky /tmp as the namespace parent

[rldyourmnd]

Problem

install --apply could not succeed on any ordinary system:

[error] product coordination namespace parent must be owned by the current user

coordination_root() is Path("/tmp") / f"nddev-zcode-app-bootstrap-locks-{uid}", and creating it opens /tmp and requires the current user to own it. /tmp is root-owned everywhere, so the namespace could never be created and every apply stopped before touching anything.

Only a target whose namespace already existed kept working — which is why this survived. The failure is invisible until the first genuinely fresh install. Reproduced here with no /tmp/nddev-zcode-app-bootstrap-locks-1000 present.

Why ownership was the wrong test

A shared temporary root is root-owned by design. What makes it safe to create a per-uid directory inside is the sticky bit, which stops one user removing or replacing another's entries.

The check now accepts exactly that shape — root-owned and sticky — and nothing looser, at both the initial validation and the re-validation held for the duration of the transaction (the second one produced the follow-on must remain owned by the current user failure).

Everything else still demands current-user ownership, including the namespace directory itself, which stays 0700 and private.

Verification

From a normal layout — sandboxed HOME, TMPDIR=/tmp, no pre-existing namespace:

[info] mode: APPLY
[ok] marketplace: nddev-builder
status: state=managed  setup_id=nddev-builder  posture=full-auto
~/.zcode: AGENTS.md  skills  cli  v2  NDDEV-POSTURE.json  BUILD-VERSION

• cli-tools/validate_public_contracts.py — PASS
• run_harnesses.py --module nddev-zcode-app --lane fast — PASS
• run_harnesses.py --module nddev-zcode-app --lane platform --platform ubuntu — PASS
• ruff check / ruff format --check clean

https://claude.ai/code/session_017fG88hR3mfP7YMFABzbKPB